Josephine Tey 
The Singing Sands 

On his train back to Scotland for a well-earned rest, Inspector Grant learns that a fellow passenger, one Charles Martin, has been found dead. It looks like a case of misadventure – but Grant is not so sure. Teased by some enigmatic lines of verse that the deceased had apparently scrawled on a newspaper, he follows a trail to the remote Outer Hebrides.
And though it is the end of his holiday, it is also the beginning of an intriguing investigation into the bizarre circumstances shrouding Charles Martin”s death…